In many of the suburban areas, these neighborhoods are filled with young families. Kids still play in the streets, especially in these types of neighborhoods off the beaten path.
The parents probably had eaten, and their daughter was outside playing. A cool front has come through North Texas and it has been very pleasant the past few evenings.
7:30 - 7:45 is when it is getting dark here. Parents would start calling their kids from outside. After about 10 minutes, they'd start looking, possibly walking up and down a block or two. Then, they'd start calling friends if they couldn't find the child.
I can see a kid playing outside, alone, a person comes upon them and a crime of opportunity presents itself to one so inclined. This area is near enough rural fields that someone could take a child and move to a vacant field fairly quickly.
Looking at Google street view, there are a lot of red pickups in the 2-3 block area near the child's home.
Hopefully that green splatter of paint doesn't wash off easily.
The tarp will play a part. They either had to purchase a tarp, or had one in the truck already. If they were a painter, they would have the tarp already. I'd look at people in the area where the child lived who were having their houses painted, especially the exterior. That would be about the time of day someone would be finishing up a paint job. That would explain the paint spot on the truck and having the tarp. They should also check area stores that sold a tarp between 7:00 and 8:45 Monday evening.
